1. Field of the Invention
This invention relates to components for electroluminescent devices. In particular, this invention relates to polymeric coatings for the components, which provide enhanced environmental protection for the components.
2. Description of the Related Art
Electroluminescent (EL) lamps are an attractive alternative to conventional lighting systems, especially for display and backlighting devices. A typical EL lamp consists of a dielectric layer and a light-emitting phosphor layer sandwiched between two conductive surfaces, a transparent front electrode, and a rear electrode. The primary purpose of the dielectric layer is to allow the lamp to withstand higher voltages without shorting between the conductive surfaces. The phosphor layer comprises phosphor particles, typically zinc sulfide or other phosphorescent particles known in the art, suspended in a polymeric matrix. The transparent electrode comprises a transparent ceramic, typically indium tin oxide (ITO).
One of the major technological barriers to the widespread use of EL lamps has historically been the sensitivity of the lamp components, particularly the phosphor particles and the electrode, to environmental conditions such as moisture. In addition, ITO electrodes are relatively unstable and may be susceptible to electrochemical reduction during lamp operation. Improvements in the adhesion of ITO electrodes to the phosphor layer are also desireable.
One method of protecting EL lamp components from moisture is to shield the entire EL lamp assembly in a fused, water resistant (polychlorotrifluoroethylene) envelope. However, this method limits the configurations that the EL assembly may attain.
Another method of protecting the phosphor particles is by the microencapsulation of each individual phosphor particle in a glass-like ceramic coating, as described in U.S. Pat. Nos. 5,593,782; 5,439,705; and 5,418,062 to Budd. Attempts to attach pre-formed, organic polymers to the phosphor particles, however, result in only a very small amount of the polymer being immobilized onto the phosphor surface, as once the surface is becoming significantly covered, additional polymers, which are trying to reach the surface, have to diffuse against the concentration gradient built up by the already deposited polymer chains. Polymer layers formed by such a xe2x80x9cgrafting toxe2x80x9d technique is therefore intrinsically limited to low graft density and low film thickness.
There accordingly remains a need in the art for alternative approaches for the protection of EL lamp components such as phosphors and ITO electrodes. There further remains a need for methods to improving the adhesion of ITO electrodes to the phosphor layer.
The above discussed and other drawbacks and deficiencies of the related art are overcome or alleviated by a protective coating for electroluminescent device components, particularly for metal parts such as phosphor particles and electrodes, comprising a hydrophobic, organic polymer.
In one embodiment, the electrode is indium tin oxide and the organic polymer is a linear polymer formed by ring opening metathesis polymerization.
In another embodiment, the phosphor is zinc sulphide and the organic polymer is a linear polymer formed by ring opening metathesis polymerization, wherein the linear polymer is attached to the phosphor by a tethering layer.
The polymeric organic, hydrophobic coating may accordingly be manufactured by the attachment of a functional group or a functionalized tethering layer to the surface of the components, followed by polymerization of the coating from the functional groups. Polymerization from the functional groups may be carried out by any chain polymerization process, including ring-opening metathesis, wherein the functional groups are first derivatized with a catalyst, followed by polymerization to form the hydrophobic coating.
This method overcomes certain steric and diffusional barriers usually encountered in the coating of components with organic polymers. Unlike other methods, a dense coating is formed, which greatly enhances the protective quality of the coating. The above discussed and other features and advantages of the present invention will be appreciated and understood by those skilled in the art from the following detailed description and drawings.